1. Field of the Invention
The invention pertains to the field of coal hydrogenation and techniques based on coal hydrogenation especially relating to recovery of valuable volatile components from coal hydrogenation products.
2. Background of the Invention
Coal hydrogenation methods are known wherein the coal is hydrogenated by reaction with hydrogen at 250 to 550.degree. C. (preferably 350.degree. to 490.degree. C. and pressures of 50 to 700 bar (preferably 100 to 350 bar), particularly in the presence of catalysts. At room temperature the products comprise solid residues and highly viscous liquid residues, along with liquid and gaseous hydrocarbons. Either coals or lignites or both may be employed in the hydrogenation (see Kroenig, W., 1950, "The catalytic hydrogenation of coals, tars, and mineral oils", Springer Verlag, Berlin, Goettingen, Heidelberg). The associated technology was developed to the feasible stage in the years 1920 to 1945, and was put into practice. The basic processes are those known as the Bergius-Pier and Pott-Broche methods.
New techniques building on these processes have been developed recently and have been tested on the bench or pilot scale. These include the EDS-Technology, SRC, H-Coal, and Neue Deutsche Technolgie processes. The latter has been undergoing testing since 1981 in the Bottrop large scale research facility (see Frank, H. G. and A. Knop, 1979, "Coal refining", Springer Verlag, Berlin, Heidelberg, New York, pp. 228-251).
All these processes have the common feature that the hydrogenation residues are separated from the gaseous and liquid products in hot separators wherein the phase separation takes place at the pressure and temperature of the reaction, or at the pressure of the reaction and at temperature slightly below the reaction temperature employed. In this connection the further processing of the hydrogenation residues is of interest, since these residues comprise valuable particular volatile product oils, in additon to solid materials such as unconverted coal, ash, catalysts, and non-volatile liquids or viscous intermediate products such as asphaltenes and pre-asphaltenes. The said valuable volatile product oils should be separated out to increase the yield of liquid products.
Low temperature carbonization or vacuum distillation is employed, among other methods, to separate out these volatile oil components in the residue. The oils recovered may be employed as slurry oils or slurry oil components for the process coal employed in the hydrogenation process. The low temperature carbonization is carried out in spherical furnaces or screw furnaces. The volatile oils themselves decompose pyrolytically during the carbonization process, so that valuable products of the hydrogenation are lost. The volatile oils can be separated out by vacuum distillation of the hydrogenation residue. The oils recovered are valuable as comminution oils. They also may be further hydrogenated under relatively mild conditions. However, there are substantial problems associated with the handling of the residue from the vacuum distillation. It is very difficult to remove from the vacuum distillation column and to transport for further processing, due to the high viscosity of the material and high solids content.